Connectors of the type known as circuit board mount jacks typically are used to provide electrical connection between multi-conductor cables and printed circuit boards. One popular type of cables, known as untwisted shielded pair ("UTP") cables, typically includes a plurality of unshielded twisted wire pairs. Common mount jacks for such cables usually comprise an insulative housing which includes two rows of electrical conductors. One end of the conductors provides a female mating section for electrical connection with a plug of the cable, while the other end comprises a plurality of solder pins that are adapted to be soldered to a printed circuit board.
As known in the art, undesired portions of desired signal power can be coupled to the individual conductors of adjacent conductor pairs in mount jacks when an electrical signal of a given frequency is transmitted therethrough. This coupling is due to the mutual capacitance and mutual inductance between adjacent pairs of conductors that are not in balance, thus yielding a residual coupling termination. This property results in crosstalk. The extent of the crosstalk is governed primarily by geometrical orientation and in particular by the spacing and angular orientation of the offended line pair. Crosstalk also will depend upon the constituent parameters of the intervening volume, such as dielectric constant and magnetic permeability. Furthermore, the extent of the crosstalk is a function of the frequency of the offending signal. Crosstalk usually increases logarithmically as the frequency of the signal increases and commonly is expressed as 10.times. log of the ratio of the offended pair crosstalk power divided by the offending pair signal power (decibels or dB).
As electrical connectors such as circuit board mount jacks are utilized more frequently in high frequency data and communication applications, the crosstalk that arises in the adjacent and parallel contacts of the jack has become a problem in the industry. This problem is exacerbated due to the trend toward miniaturization as well as due to FCC rules which require less than optimal orientation of the contacts within the jacks. In an effort to minimize the effects of such crosstalk, standards have been developed in the industry for controlling crosstalk. For example, in category 5 of ANSI/TIA/EIA, it is required that a connector exhibit a pair to pair nearend crosstalk ("NEXT") loss which does not exceed 40 dB at 100 MHz. Since 25 pair miniature connectors are designed to carry six times the signals of ordinary four pair cable, this requirement should be met on a more stringent power sum basis (i.e., category 5E) since, for each pair, crosstalk couplings from all the other pairs must be considered.
Previous solutions to the crosstalk problem have provided mixed results. In one such solution, a crosstalk compensation circuit is positioned on the printed circuit board external to the circuit board mount jack. However, such an arrangement creates certain problems: (a) the compensation circuit occupies valuable real estate on the printed circuit board; (b) openness of the compensation susceptibility to other induced field interference (e.g., EMI); and (c) adequate compensation is made incrementally more difficult by the distance from which the compensation circuit is spaced from the source of the crosstalk. In another solution disclosed in U.S. Pat. No. 5,562,479, issued to Passas and Winings, crosstalk compensation is provided within a 25 pair connector. In particular, the connector comprises a mandrel portion in which the individual conductors of the connector are arranged in an orientation to compensate contact area crosstalk. Although the mandrel provides for substantial crosstalk compensation, the amount of compensation can be inadequate because the connector lead frame itself behaves as a source of crosstalk. As for other techniques conventionally used to limit the effects of crosstalk, these techniques often suffer from a deterioration of crosstalk compensation.
From the above, it can be appreciated that it would be advantageous to have an electrical connector, such as a circuit board mount jack, that includes internal crosstalk compensation and that satisfies category 5E of ANSI/EIA/TIA.